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Product Description
In 2011, audio engineer NwAvGuy published a blog post titled “O2 Headphone Amp,” in which he outlined his philosophy on defining sound quality and detailed his ideal audiophile circuit design. Our version of NwAvGuy's famous O2 amplifier, the Objective 2 Desktop Edition features updates based on feedback from the community Read More
I am by no means an audio gear expert, but I have the O2 amp and HD 6XX (the combination you mentioned). O2 has a headphone jack (to plug in your headphones), a port (for power), and RCA cable inputs. So, the only possible inputs to the amp are RCA audio cables (For Left and Right channels, in white and red). So, how do we connect the music source to the amplifier? One possible way is, use a 3.5mm to 2-Male RCA Adapter cable. But I am not sure if the audio quality will be clear, since music will be amplified but the clarity will be as good (or bad) as the in-built DAC in your laptop/desktop or phone. It makes sense to buy a DAC, from all the sources I have read. You can buy the 3.5 mm to RCA cable for 9$, and check the audio quality (Frankly, I have not checked it too, though I assume it should work). I am using 2 devices as DAC. End-to-end connections:
(1) Laptop (source) -- > Centrance DACport HD (DAC) --> Objective 2 (Amp)--> Headphones (Senn HD 6xx)
Apple Mac --> Centrance's USB 'slot' =Centrance= Headphones 'slot' ---> 3.5mm 2-Male RCA Adapter cable to the Objective 2 amplifier --> Headphones.
(1) DAP (source and DAC) --> Objective 2 (Amp)--> Headphones (Senn HD 6xx)
Shanling M0 (Headphones slot) ---> 3.5mm to 2-Male RCA Adapter cable --- > Objective 2 amplifier --> Headphones.
The DAP acts as a DAC since it has a very good DAC chip.
I connect HD 6xx directly to it too. It works great (as loud as I can handle, and very clear). I almost don't need an amp.
tonsoNot a huge difference, but it is definitely perceptible. 'Better' is subjective, so I will say this - The clarity is as per the source and DAC, so with the amp (Objective 2), I have room for some more volume. Dacport HD on its own is clean and loud, but I have it at max volume at high gain when using the Senn HD 6xx. Adding O2 to the mix, I still go to high gain, but I stop short of the max volume (say 75 to 80%). This is pretty loud for me, and I listen for shorter periods.
Note - I am 43 yrs old. If you are a decade (or more) younger, you might need lesser volume than me, with any setup (to hear the equivalent loudness).
In hindsight, these buys were learning/experimental decisions (I cant return since I am from India, far from USA). Would I buy this combination today? Not at all. I might buy a good sub 90$ DAC (Topping D10, SMSL 10th MKii) and a powerful sub 100$ amp (Magni Heresy or JDS Labs Atom - 99$). And retain the Dacport HD - that's a keeper (for 100 ohm to 300 ohm phones + portability).
HD 6XX are known present quite a bit of detail, and the amp is quite clear. So if you have interference, hisses or jitters etc, getting fed into the amp, then it'll pass them into the HD 6xx, and the HD 6XX will pass them onto you.
I was using HE 4XX headphones, and this amp, plugged into my PC, without a DAC, for months, without noticing any such artifacts. I ended up listening closely for that kind of thing earlier this year ( a friend asked me to check a couple of her voice acting recordings ) , and a that point I started to notice a little background hiss, especially when the PC was doing more processing. So that's why I bought a DAC.
My advice is to do without a DAC at first, then if you happen to notice artifacts from whatever the amplifier is connected to, consider getting a DAC to eliminate them.
That way if you don't get a DAC, that's money saved. If you do get a DAC, you'll appreciate what it does better.
(I went with a Cyrus Soundkey, about £65, goes to 24 bit 96kHZ which is plenty for my games and MP3 files, and seems to have done the job.)
The different gain stages are just about multiply the amount of voltage applied and amplifying the initial preamp signal more. Both the hd6xx and k7xx are relatively easy to drive dynamic headphones so both should be okay on the 2.5x/low gain mode of the standard model. It's possible that the 6xx may need to be moved to the higher mode but as the O2 is such a neutral amplifier the gain stages don't change the sound so it's simply a matter of you going "I've turned the volume past half way and it's not loud enough so I'll turn up the gain". Completely up to if you need the extra volume or not.
According to some comments and the product pics it seems like the product isn't available with the EU plug. You can choose either the 120V USA plug or the 240V USA plug. You will either need to buy an adapter or a new power cord and transformer.